Gas pressure blasting device



F. H. ARMSTRONG l' AL GAS PRESSURE BLASTING DEVICE Filed Nov. 24, 1947 Oct. 24, 1950 fak/.aen C f/srez/Je JNVENToRs.

Wmv TTOZIVEYS.

`Patented Oct. 24, 1 950 GAS PRESSURE BLASTING DEVICE E Frank H. Armstrong, hicago, Ill., and Edward C. Filstrup, Jr., St. Joseph, Mich., assignors to `Armstrong Coalbreak Company, Benton Harbor, Mich., a corporation of Michigan Application November 24, 1947, Serial No. 787,734

(o1. 1oz-25) 17 Claims.

This invention relates to improvements in gas pressure blasting devices, and more particularly to blasting devices used in mining kor breaking down coal and like material without requiring combustion.

In general the instant device is of that type provided with a chamber into which a gas, such as air, is introduced while the chamber is positioned in a mine bore juxtaposed to an undercut formed in the coal or other ore to b'e mined. The source of gas pressure, such as a gas pump, may be located remotely at a safe position spaced/from the blasting chamber and is connected to the chamber by a suitable gas-conducting conduit. The chamber has outlet ports which are contolled by a valve to close the same while gas is being introduced into the chamber. The valve is held in closed position by a member of a strength which will permit it to withstand a predetermined pressure. When the' gas pressure within the chamber builds up to a value exceeding the pressure which the valve stop member will sustain, the member is ruptured, broken or sheared, thereby releasing the valve which moves in response to pressure acting thereon to a position at which the discharge outlets are opened. The opening action occurs in a very short interval of time so that there is a sudden release of the gas confined in the chamber, which release is in the nature of a blast that is effective to break down the coal, ore or other material around the bore in which the chamber is located.

While devices of this type are intended for reuse by installing a new rupturable or sharable member and re-setting and re-charging the device, 'they are subject to wear, particularly at the pressure seals, by virtue of the conditions under which the device is used. Thus the breaking of coal or ore incident to the blast created by the device creates dust and dirt particles around the device which enter the chamber after a blast has occurred. These particles have an abrasive action which quickly destroys the seals necessary to retain the high pressure of the charge. These conditions have ma'de it necessary in previous devices to rely primarily upon metal-tometal seals which have required very close tolerances of parts and have rendered the devices expensive. However,- metal-to-metal seals are subject to scoring and the life span of the parts has been short because the scoring occasioned by dust and dirt destroys the metal-to-metal seal to the extent that leakage occurs which renders the device inoperative or not economical.

Therefore, it is the primary object of the invention to provide a device of this character with novel, soft, flexible sealing means and protective means cooperating therewith and with a. valve to protect the seal at all times against access oi dirt and dust thereto, l

A further object is to provide a device of this character having a metal chamber and a metal valve plug with soft, flexible sealing means, such as rings interposed between said valve and chamber. to eiectively prevent leakage of air between said parts without requiring pressuretight ts between said metal parts.

A further object isto provide a device of this character having a metal body and a metal sleeve valve adapted normally to close discharge ports g in the metal body, sealing means carried by said body and engaged by said valve, and a follow-up sleeve shiftable in one direction responsive to 1fluid pressure in the chamber or body and adapted to shift to a position to cover and protect said seal when said valve moves away from said seal incident to opening of said body or chamber discharge ports.

A further object is to provide a device of this character having a protective sleeve normally shiitable in one direction by pressure in a chamber and having a seal between the same and the chamber with a vent to maintain pressure outwardly of said sleevel at atmospheric value to avoid interference with operation of said sleeve responsive to the pressure acting thereon.

A further object is to provide a device of this character with means for lubricating the working parts thereof without interfering with the seal between such parts.

Other objects will be apparent from the following specification.

In the drawing:

Fig. 1 is a longitudinal axial sectional view of the device taken on line I- I of Fig. 3 and illustrating the device in its charging position.

Fig. 2 is a fragmentary longitudinal sectional view taken on line I-I of Fig. 3 and illustrating the device in pressure-releasing cr blasting position.

Fig. 3 is a transverse sectional view taken on line 3 3 of Fig. 1. Y

Fig. 4 is a transverse sectional view taken on line 4 4 of Fig. 1.

Referring to the drawing which illustrates the preferred embodiment of the invention, the numeral I0 designates an elongated tubular body formed of metal of a strength to contain gas under high pressures. for example, pressures of from 10,000 to 15,000 pounds persquare inch 'I'he length of the body may be in the order of 50 inches, although this dimension is illustrative and not intended to be limiting. The outer diameterof the body is such that it may ilt freely within a bore drilled inthe face of the material, such as coal, to be mined or broken down, it being understood that a horizontal undercut is preferably first formed in the working face and the bore is located thereabove in the manner well understood in the art. The opposite ends of the body I are preferably provided with neck portions II of slightly reduced diameter. One end of the body I0 mounts a cap I2 which has an internally screw-threaded neck portion I3 engaging and secured to the threads of said neck. An annular groove is formed in the head I2 of a diameter to confront the end edge of the adjacent neck II and mounts an 0 ring I4 or any other suitiable sealing means. The cap I2 has a reduced screw-threaded central opening therein communicating with a socket formed at the outer end thereof. The socket isadapted to receive a fitting I5 having a neck I6 screw-threaded in the cap. The outer end of the fitting I5 has a socket in which the flared end of a gas supply tube I1 extends and in which said tube is anchored with a wedge it by means of a fitting I8. The tube or conduit I1 is preferably elongated and extends to a source of supply of gas under high pressure which may constitute either a compressor or a large container for gas at high pressure. The gas in each instance is preferably air, although other types of gas may be used. The fitting I5 has a central or axial bore I9 extending therethrough and communicating with the conduits I1. head I2 is preferably substantially equal to the exterior diameter of the main portion of the body I0.

A rigid tubular end member whose diameter is preferably substantially equal to the large dlameter of the body I0 is screw-threaded upon the neck II at the opposite end of the body I0 and projects outwardly from said body. The member 20 has a series of radially spaced outlet openings 2I formed therein intermediate its length and spaced from the end of the body I0, with the axes of said openings inclined relative t0 the axis of the body Il) and to the perpendicular. Thewall thickness of the tubular end member 20 at the end thereof threaded upon the body I0 is reduced to provide an enlarged inner diameter at said end which terminates in a shoulder 22. A ring 23 fits within the end vmember 20 and bears against the end of the adjacent neck II of the body I0. This ring 23 has an annular groove in one end face thereof which receives an 0 ring 24 or other suitable sealing means bearing against the end of the neck I I to form a seal. The opposite end of said ring is of stepped form having a reduced outer diameter and bears against an annulus 25 which preferably seats against a shoulder 2B formed in the tubular member 20. The inner diameter of the annulus 25 is preferably-substantially equal to the inner diameter of the ring 23. An 0 ring 21 fits around the reduced end portion of the ring 23 and is retained in said position by the annulus 25. One or more ports are formed in the member 20 in register with the ring 23 and have screw-threaded plugs 28 mounted therein to seal the same, said ports being provided for the introduction of lubricant around the ring 23. A plurality of spaced circumferential grooves are formed in the amasar The exterior diameter of the inner surface of the member 20 between the shoulder 22 andathe outlets 2| thereof. Each of these grooves receives an 0 ring 29, and one or more screw-threaded ports in the member 20 communicate with each groove for the purpose of inserting a lubricant, and are adapted to be sealed by a plug 30. A port is formed in the member 20 between the grooves receiving the 0 rings 29 and mounts a spring-pressed check valve 3l normally held sealed by the spring thereof but adapted to be unseated by an outwardly directed fluid pressure to vent the member 20. This check valve may be of any suitable construction. An interior circumferential groove 32 is formed in the member 20 adjacent to the outlets 2I but oppositely arranged with respect to the grooves mounting the O rings 29. The groove 32 receives an O ring 33. A threaded port communicates with the groove 32 and receives a screwthreaded removable seal or plug 34.

A cylindrical sleeve valve 35, of a length slightly greater than the longitudinal spacings of the 0 rings 29 and 33 on the opposite sides of the outlets 2|, ts snugly and slidably in the bore of the member 2U and is adapted to seal said outlets in its charging position illustrated in Fig. 1. The opposite end portions of this valve are effectively sealed by the constrictive engagement of said 0 rings 29 and 33 therewith. The valve 35 has a central elongated outwardly projecting stem 36 of a length greater than the spacing between the outlets 2I and the free end of the member 20. A plug 31 is screw-threaded in the free end of the member 20 and bears against a shoulder 38 of member 20 at its inner end. The plug 31 preferably has a circumferential groove in its inner end receiving an 0 ring or other seal 39 which bears against the shoulder 3B. The plug 31 has an -axial bore therethrough of a diameter having a snug sliding fit around the shank 36 of the sleeve valve 35 and is interiorly grooved intermediate its length to receive an O ring 39', there preferably being a bore 40 extending transversely through the member 31 into communication with the O ring groove and being sealed by a removable plug 4I at its outer end. The plug 31 has a diametrically extending opening or passage 42 extending therethrough. A shear pin 43 is adapted to be received in said passage 42 and the end of the valve stem 36 bears thereagainst when the valve is in sealing position and ready for charging, as illustrated in Fig. 1. The outer end of the plug 31 has an enlarged axial screw-threaded bore in its outer end, whose inner end communicates with the passage 42. A clamp member 44 is threaded in said last named bore so that its inner end will bear against and clamp the shear member 43 xeclly in the passage 42 in which said shear member normally has a loose or free. t. The clamp member 44 has an axial bore 45 of a diameter to permit the valve shank 36 to slide freely therein.

The inner end of the plug 31 has a concentric socket 46 formed therein and receiving snugly a sleeve 41 which projects inwardly beyond the end of the plug 31 as shown. The sleeve 41 serves to confine the end portion of one or more coil springs 48 which encircle the shank 36 and bear at their opposite ends against the head of the sleeve valve 35. Thus the normal position of the sleeve valve is its outlet sealing position illustrated in Fig. 1. The outer diameter of the sleeve 41 is preferably slightly less than the inner diameter of the sleeve valve 35 and thus provides an annular socket 49 into which the sleeve valve 35 may slide. as illustrated in Fig. 2, for purposes to be hereinafterset' forth. In this connection it will be observed that the inner diameter of the member between the groove 32 andthe shoulvder 38 is slightly greater than the diameter of said member between the groove 32 and the .outlets 2|, and also that the outer edge of the end of the sleeve valve facing the plug 31 is slightly tapered.

A follower sleeve 50 ts within the member 20 slidably between the sleeve valve 35 and the annulus in the Fig. l position of the parts and normally bears against the sleeve valve 35. The follower sleeve 50 fits snugly and slidably in the member 20 to have a sealing engagement with at least the two right-hand O rings 29 as illustrated. The end portion 5| of the sleeve 50 adjacent the ring 25 is preferably outwardly flared to have av snug t in the enlarged bore of the member 20 at the right of the shoulder 22 thereof and is of a length whereby said enlarged portion 5| is spaced `from said shoulder 22 in thecharging position the sleeve shoulder 5I and the shoulder 22 of the member 2U. If desired, one or more vent ports 52 may be provided in the sleeve 50 in register with the annular space between the shoulders22 'and 5| and in register with one or more of the grooves receiving the 0 rings 29.

In the operation of the device, the valve is locked in its sealing position by pressing inwardly against the valve stem to .position the outer end of the stem inwardly beyond thev opening 42 in the plfug 31 and then inserting the shear member 43 through the opening 42 to span the bore thereof and restrain the stem against outward displacement from its Fig.` 1 position at which the valve 35 is in sealing position. The clamp 44 may be tightened to lock the pin 43 in the opening 42. It will be assumed, lof course, that the conduit I1 is connected with -a source of supply of gas under pressure. The unit so'conditioned advantage in the device and insures against they in a blasting action. -The movement of the valve occurs very rapidly and is somewhat cushioned by the springs 48. However, where the blasting pressure is high, for example, 'a pressure of 5,000 pounds per square inch or more, the sudden release of the valve upon shearing of the member 43 moves thel valve 35 so rapidly and with such force that the cushioning action of the springs 48 is not adequate to prevent injurious impact. Such impact is prevented, however, by the construction of the parts shown which entails the entry of the lefthand end of the sleeve valve 35 into the annular pocket 49 between the member 20 and the sleeve 41 and the snug fit of said parts which causes the building. up of high pressure within the .pocket 49 in advance of the sleeve valve adequate to prevent impact of the sleeve valve with the end plug 31 incident to the opening movement of the valve. The quick -opening of the valve is desirable to secure as nearly an instantaneous discharge of the gaseous charge through the outlets 2| as is possible, and this quick discharge is one of the advantages securedl by the instant device.

It will be apparent that when the valve 35 is opened, the 0 ring 29 engaged by the right-hand end when the valve is sealed, normally will be left exposed. The exposure of the 0 ring to the high pressure in the device would be injurious thereto, and is avoided in the instant construction by the provision of the sleeve 50. The area of the left-hand edge of the sleeve 50 is much smaller' than the area of the opposite end edge of member 50. The diierence in area of these end edges when subjected to the same pressure causes the sleeve 50 to be urged to the left to the limit permitted by the shoulder 22.-f' In other words, movement of the sleeve 50 tothe left occurs until the flange or enlargement 5| of the sleeve strikes the shoulder 22. This movement is adequate to permit the sleeve 50 to follow the sleeve valve as it moves away from the left-hand 0 ring 29, thereby .permitting said sleeve to span said O ring groove to seal and protect the 0` ring. fromtlie .pressure of the gaseous charge as illustrated in Fig. 2. 'I'his is of substantial possibilityv of injury to theO ring or other sealing means. It will =be apparent that an O ring vor other flexible sealing member affords a seall ing actionmuch superior to the sealing action is then, inserted into the bore Ain the coal or other material to be broken down and the device may be tamped in place by materialinserted in the bore behind the device inthe manner well understood in the art,l if desired. Grasun` der pressure is then discharged into the bodyA I0 from the conduit |l through the passage I9 to charge the device. The shear member- 43 is selected to withstand any given pressure above vatbetween engaged metal parts and further that it permits more clearance between the metal partsy than is possible in a metal-to-metal seal. kThis frees the parts and also lowers the manufacturing tolerances of the parts, thereby reducing manufacturing costs. With the instant construction, any tendency inherentfin an O ring mcspheric pressure, that is, it is selected to withstandv pressure below blasting pressure and to shear at desired blasting lpressure. It will be understood,. of course, that theremaining parts of the device are all designed to withstandv vpressures greater than the selected blasting pressure. When the'pressure withinl the device has been build up to a'point exceeding the pressure which thevshear memberv 43 will withstand, said member is sheared by the valve stem 36 incident to the application of rsaid pressure `against the end of the 'sleeve valve, thereby freeing the sleeve valve 35 for movement to the left to the position illustrated in Fig. 2. 'I'he `outlets 2| are thus c-pen:d for quick exhaust of the blasting pressure or other flexible device to be extruded or subject to cold flow in the lpresence of high pressures is entirely overcomeby the fact that the seal is protected at all times and in all -adjustments or conditions of the device against the effect of high 'l gaseous pressures acting thereon.

A further advantage of the construction is that it protects said O rings and seals against access thereto of the dust or dirt generated incident to the blasting. s f y Other advantageous features of the instant device are the provision of the check valve 3| which permits venting of any press-ure which may leak into the area between the tubular member 20 and the sleeve 50 with which said valve.

communicates and the provision of the ports normally sealed :by ,the removable plugs 30 through which lubricant may be introduced to facilitate the relative movement of the valve 35 and the follow-up sleeve 50 with respect to the tubular member 20.

Another advantageous function of the check valve 3| is to provide means for venting or discharging any dirt which might work its way into the space between tubular member 20 and the sleeve 50 with which said valve communicates. In other words, whenever there is a pressure in said space which is above atmospheric pressure, the opening of the valve permits the escape of air which would carry any entrapped dirt therewith. l

It will be understood that while the various seals, such as lll, 24, 21, 29, '33, 39 and 39', have been described herein as rings, this description is intended to be descriptive and not limiting, and any other type of ilexible soft seal or gasket ring may be used in place of an O ring.

While the preferred embodiment of the invention has been illustrated and described herein, it will be understood that changes may be made therein within the scope of the appended claims without departing from the spirit of the invention. v

I claim:

l. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing a charge of gas under pressure at one end/ of said housing, the oppvosite end of said housing having an end Wall provided with intersecting longitudinal and transverse passages, a pressure responsive piston slidable in said housing and normally positioned in spaced relation to said end wall to span and seal said outlet, a piston rod projecting into said longitudinal passage, and a shear pin received in said transverse passage and engaged by said piston rod.

2-. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing a charge of gas under pressure at one end of said housing, the opposite end Aof said housing having a bore therethrough, a pressure responsive member slidable in said housing and having a part slidable in said bore, said member being adapted to span and seal said outlet, and a locking member positioned exteriorly of the housing chamber and engaged by said part in position to permit saidmember to seal said outlet, said locking member yielding in response to a predetermined pressure to release said pressure responsive member from outlet sealing position. v

3. A blasting device comprising a chambered housing having a lateral outlet intermediate its housing and encircling opposite ends of said valve,

`said valve shifting out of engagement with one sealing member upon release Vof said positioning means, and a protective member in said housing shiftable into protective engagement with said last named sealing member incident to release of said valve,

4. A blasting device comprising a chambered houing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of gaunder pressure, a pressure responsive sleeve valve slidable in said housing, means.V

yielding in response to a, predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shifting out of engagement with one sealing member upon release of said positioning means, and a protective member in said housing shiftable into protective engagement with said last named sealing member incident to release oi.' said valve, said sealing members being seated in circumferential grooves formed in the interior of said housing.

5. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of gas under pressure, a pressure responsive sleeve valve slidable in said housing, means yielding in response to a predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shifting out of engagement with one sealing member upon release of said positioning means, a protective member in said housing shiftable into protective engagement with said last named sealing member incident to release of said valve, said protective means constituting a pressure responsive sleeve, and a stop on said housing for limiting shifting of said protective sleeve in a position spaced from said outlet.

6. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of gas under pressure, a pressure responsive sleeve valve slidable in said housing, means yielding in response to a predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shiftin'g out rof engagement with one sealing member upon release of said positioning means, a protectivev member in said housing shiftable into protective engagement with said last named sealing member incident to release of said valve, said protective means constituting a sleeve having an outwardly projecting circumferential ange at one end providing a larger surface area at said end than at its opposite end, and a stop on said housing engageable by said flange at a predetermined seal protecting position of said sleeve.

7. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of gas under pressure, a pressure responsive sleeve valve slidable in said housing, means yielding in response to a predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve. said valve shifting out of engagement with one sealing member upon release of said positioning means, a protective member in said housing shiftable into protective engagement with said last named sealing member incident to release of said valve, said protective member constituting an open ended tubular member fitting snugly in said housing and normally pressure urged in the same direction as and into engagement with said valve, and means for limiting pressure responsive travel of said protective member upon release oi said valve.

8. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of gas under pressure, a pressure responsive sleeve valve slidable in said housing, means yielding in response toa predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shifting out of engagement with one sealing member upon release of said positioning means, a protective member in said housing shiftable into protective engagement with said last named sealing member incident to release of said valve, said housing having grooves receiving said sealing members and a lubrication port communicating with each groove, and a. removable closure for each port.

9. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of gas under pressure, a pressure responsive sleeve valve slidable in said housing, means yielding in response to a predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shifting out of engagement with one sealing member upon release of said positioning means, a protective 'member in said housing shiftable into protective engagement with said last named sealing mem-ber incident to release of said valve, and at least one seal carried by said housing and encircling said protective member in all positions thereof.

10. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of gas under pressure, a pressure responsive sleeve valve slidable in said housing, means yielding in response to a predetermined pressure for normally positioning said valve to span vsaid outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shifting out of engagement with one sealing member upon release of said positioning means, a protective member in said housing shiftable into protective engagement with said last named sealing member incident to release of said valve, and a pair of spaced seals carried by said 4 yielding in lresponse to sive sleeve valve slidable in said housing, means a predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shiftingfout of engagement with one sealingmember upon release of said positioning means, and a protective member Vin said housing "shiftable into protective engagement with said last named sealing member incident to release of said valve, said housing having an annular socket at one end to receive said valve and cooperating therewith to dene a substantially sealed cushioning chamber when said valve moves to release position.

13. A blasting device comprising a. chambered housing having a lateral'outlet intermediate its ends, means for introducing into said housing a charge of gas under pressure, a pressure responsive sleeve valve slidable in said housing, means yielding in response to a predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shifting out of engagement with one sealing member upon release of said positioning means, a protective member in said housing shiftable into protective engagement with said last named sealing member incident to release of said valve, and a spring normally urging said valve to sealing position.

14. In combination, `a tubular member hav- Y ing a lateral outlet intermediate its ends, a valve housing adjacent said last named sealing member and encircling said protective member in all positions thereof, said housing having a vent between said seals.

11. A blasting device comprising a chambered housing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of gas under pressure, a pressure responsive sleeve valve slidable in said housing, means yielding in response to a predetermined pressure for normally positioning said valve to span said outlet, yielding sealing members carried by said housing and encircling opposite ends of said valve, said valve shifting out of engagement with one sealing member upon release of said positioning means, a protective member in said housing shiftable into protective engagement with said last named sealing member incident to release'of said valve, a pair of spaced seals carried by said housing adjacent said last named sealing member `and encircling said protective member in all positionsl thereof, said housing having a vent between said seals, and a vent.

12. A blasting `device comprising `a'. chambered spring pressed check valve in said housing having a lateral outlet intermediatev its ends, means for introducing into said 'housing a charge of gas under pressure, aV pressure responhaving a, snug sliding fit in said member and adapted to span said outlet, circumferential seals carried by said member on opposite sides of said outlet and encircling said valve-when the same ,is in operative outlet-sealing position, and a follow-up sleeve fitting snugly in said member and having a limited travel therein to a position protecting the seal released by said valve incident to opening `movement of said valve.

l5. In combination, a tubular member having a lateral outlet intermediate its ends, a valve having a snug sliding ft in said member and adapted to span said outlet, circumferential seals carried by said member on opposite sides of said outlet and encircling said valve when the same is in operative outlet-sealing position, and a follow-up sleeve tting snugly in said member and having a limited travel therein to a position protecting the seal released by said valve incident to opening movement of said valve, said sleeve being shiftable in response to fluid pressure in said member.

16. In combination, a chambered housing having a lateral'outlet intermediate its ends, a valve having a snug sliding fitin said housing and adapted to span said outlet, circumferential seals encircling oppositeends of said valve and circumferentiallyl engaging said housing on opposite sides of said outlet when said valve is in outlet-sealing position, at least one seal being carried by said'housing, and a, follow-up sleeve fitting snugly lin said housing andhaving a limited travel therein to a position protecting the seal carried by said housing and released by said valve incident to opening movement of said valve.

17. In combination, a chambered housing having a lateral outlet intermediate its ends, means for introducing into said housing a charge of fluid under pressure, a valve slidable in said housing between a normal position spanning said outlet and an open position clear of said outlet in re-.

11 v interposed between said valve and housing on REFERENCES CITED opposite sides of said outlet' and a protective The following references are of record in the member shiftable in said housing upon releasing movement of said valve and engageabie with the me of uns patent' seal for the end portion of the valve at which 5 UNITED STATES PATENTS pressure 1S applied Number Name Date FRANK H. ARMSTRONG. 2,083,734 Noble June 15, 1937 EDWARD C. FILSTRUP, JR. 2,083,736 Noble June 15, 1937 

